1. Field of the Invention
This invention relates to a break apparatus for automatic door, more particularly the brake apparatus to ensure safe and smooth closing motion of automatic door.
2. Description of the Prior Art
An automatic door is generally operated in three basic steps; transfer of the door driven by a motor to the predetermined position a little before full open or full shut position at comparatively high speed, deceleration by operating the braking means at least for once, and transfer to full open or full shut position at comparatively low speed.
Such braking means in three step operation is disclosed, for example, in Official Gazette of Japanese Unexamined Patent Publication No. Sho 58-80082.
It is necessary, however, to adjust braking power of the braking means adequately for the door of different weight or where automatic door is installed in different conditions. If not, the motion may not be smooth in some cases.
If a door is heavier than the weight suitable to certain braking power of the braking means, for example, the door speed can't be lowered sufficiently and the door is to be bumped at closing. If a door is too light, on the other hand, the door speed is lowered sharply and it takes too long time before the door is closed completely.
If operation of the braking means go out of order, the deceleration of the three steps fails and the door speed changes abruptly from high-speed to low speed or reaches the full open or full shut position while keeping high-speed, which applies impact to the door mechanism and may possibly affect the components other than the braking means.
It is desirable, therefore, to find defect of the braking means earlier.
Conventional automatic door, however, are not provided with any device to detect the defect of the braking means and the detection by persons tends to be delayed.